1. Field of the Invention
The present invention provides an improved method for the production of ethylene from a C.sub.4 or higher hydrocarbon feed. Specifically, in accordance with the invention, a higher hydrocarbon is converted over a zeolite catalyst at conditions which favor production of a product mixture containing ethylene and propylene. Ethylene is separated from this product mixture and recovered. The propylene from the reaction mixture is metathesized in order to convert the C.sub.3 olefin to further quantities of product ethylene as well as higher olefin which latter material can be recycled to the original conversion step.
2. Description of the Prior Art
Ethylene is an important chemical of commerce. In general, ethylene is largely derived from selected petroleum feed materials by procedures such as steam cracking which also produce high quantities of other materials. At times, there exist shortages of ethylene which result in uncertainties in feed supplies, rapidly escalating raw material costs and similar situations which are undesirable from a commercial standpoint. Also, due to imbalances in hydrocarbon values, economics favor using alternate feedstocks provided an effective process for forming ethylene was available.
Methods are known for the conversion of higher hydrocarbons to reaction mixtures comprised of the C.sub.2 and C.sub.3 lighter olefins. For example, published European patent applications Publication Nos. 0109059 and 0109060 provide illustrative teachings of conditions and catalysts which are effective for the conversion of higher hydrocarbons such as butenes to the lighter olefins. Copending application Ser. No. 07/343097, filed Apr. 25, 1989, likewise provides a comprehensive teaching of prior methods for the production of the lower olefins from higher hydrocarbon feed materials. In certain instances, it would be distinctly advantageous to provide means for still further improving yields of ethylene which result from the conversion of less expensive higher hydrocarbon feed materials.
The disproportionation or metathesis of olefins is likewise a known reaction. In this regard, reference can be made to Banks U.S. Pat. No. 3,261,879, to Banks "Olefin Metathesis Technology and Application," Applied Industrial Catalysis, Volume III, Chapter 7, Pages 215, et seq., Leach, Editor (1984). In addition, olefin metathesis reaction and catalysts useful therefor are described in U.S Pat. Nos. 3883606, 3915897, 3952070, 4180524, 4431855, 4499328, 4504694, 4517401 and 4547617.
Despite developments in the art, it remains desirable to provide methods for producing higher yields of ethylene from the less expensive higher hydrocarbon feed materials.